This invention relates generally to an electrode, and more particularly to a biologically compatible implantable electrode for applications such as a cardiac pacemaking or cardioversion, including heart stimulation and monitoring.
Electrodes implanted in the body for electrical cardioversion or pacing of the heart are well known. More specifically, electrodes implanted in or about the heart have been used to reverse (i.e., defibrillate or cardiovert) certain life threatening arrhythmias, or to stimulate contraction (pacing) of the heart, where electrical energy is applied to the heart via the electrodes to return the heart to normal rhythm. See, for example, commonly assigned U.S. Pat. No. 5,063,932 to Dahl et al., relating to defibrillation discharge electrode configurations and particularly to fixed planar discharged configurations, and U.S. Pat. No. 4,559,951 to Dahl et al., relating to intravascular tubular electrodes, both of which are incorporated herein by reference.
U.S. Pat. No. 5,063,932 specifically discloses an implantable cardiac electrode comprised of a planar conductive material, typically imbedded in an insulated material. Various geometric configurations of the conductive material are disclosed, taking advantage of the "edge effect" to more efficiently discharge energy.
U.S. Pat. No. 4,559,951 discloses a flexible tubular catheter assembly in which conductive coils are imbedded in the walls of the tube and connected to conductive surfaces (i.e., surface electrodes) on the tip of the catheter assembly or on the tubular surface. A catheter assembly is thus provided which allows for the use of a plurality of separate electrode surfaces without necessitating the increase in overall diameter of the catheter as additional groups of conductor coils are added.
Historically, implantable electrodes have been constructed using discrete metal parts such as rings, helically wound coils, or screens. As pacer and cardioverting devices have become more sophisticated, the electrodes therewith have also increased in complexity, and often in overall size. With each sensor system requiring a dedicated electrode, a set of electrically isolated conductors is necessary to insure sensor isolation. Where these electrodes and leads are threaded through the body's vascular system, it is important that the overall diameter of the lead and its stiffness be minimized. Also, in order to minimize trauma to the tissue adjacent to the electrode, it is desirable to reduce the surface roughness and motion at the electrode-tissue interface.
A more recent system, as disclosed in U.S. Pat. No. 4,972,846 to W. L. Gore, utilizes a laminated structure where a plated metal coating is located between two porous polymeric materials to form a patch or planar electrode. However, the use of a metal plated coating leaves the metal discharge layer subject to high localized stresses when the electrode is flexed, which in turn can cause polymeric and metallic fatigue problems. Further, the overall resistance, as well as changes in resistance level during flexing, disclosed in the Gore patent are undesirably high for a chronically implantable electrode.